Any way to un-stick the Old Sentinel?

Wrecked a very good game, on the last stage he got stuck and would not move or fire at us:

sometimes one person or more DC can get them to move again.

i was last to DC on the void’s edge when wolf was stuck and we were going to quit.

after all others left he started walking again and i finished the mission

Out of frustration we all tried multiple times.
Each character tried melee also and I tried Mike’s Air-strike many times.